The invention relates to telecommunications and more particularly to an ATM node, such as a hub, that includes local error correcting procedures.
The need for improving the integrity of the data being transmitted through large networks has continuously increased, particularly with the development of international business and other activities dealing with sensitive information.
Such concerns obviously applies to the Asynchronous Transfer Mode (A.T.M.) networks which allow transmission of data of different nature via high speed networks.
FIG. 1 illustrates an Asynchronous Transfer Mode (A.T.M.) backbone 1 which topology is comprised, for clarity sake, of hubs 10-50 which are interconnected by means of a set of full duplex opticals links 15, 16, 25, 35 and 45. The ATM networks provides with the possibility to transfer data through the format of cells based on 53 bytes, the cells being concatenated in messages as represented in FIG. 1. Assuming for instance that such a message is received by hub 10 and that this message is transferred through the network via hubs 20, 40 and 50.
Considering now that an error might occur in the transmission path. In this case, the Data Terminating Equipment (DTE) (not represented) which receives the message from the backbone via hub 50 (for instance) detects the occurrence of the error via its own Error Correcting Code (E.C.C.) mechanisms. This detection normally results in the latter discarding the full message being received, what compels the emitting DTE to send back the whole message, that is to say the full number of cells composing the message being lost in the network. It should be noticed that, should the error only affect a single cell, the full message that includes that cell is being lost, what inevitably affects the overall performance and efficiency of the system.
Therefore a need appears in the ATM technique for a solution which avoid the lost of the full message when one error occurs anywhere in the transmission path.
Additionally, since the ATM networks that exist in the world are composed of a wide variety of different elements, nodes or hubs, it is also required that newly designed hubs still present the compatibility with the already existing equipments (corresponding to huge investments which the customers wish to keep in operation as long as possible).
This problem is solved by the present invention which uses a particular ECC mechanism that is locally distributed at each level of the hubs that compose the ATM network. Therefore, each hub composing the backbone has the possibility of detecting the occurrence of an error, and to correct it. Additionally, the ECC mechanism of the present invention presents the capability of being disconnected, which allows the possibility of handling two different types of messages, comprising or not the internal ECC codes, thus allowing the use of the hub with other existing hubs which do not incorporate the ECC mechanism of the invention.
Basically, the invention takes advantage of the use of the Virtual Channel Identifier (V.C.I.) and Virtual Path Identifier (V.P.I.) for controlling an error correcting mechanism that is provided in the ATM network node.
This is performed by using a Segmentation and Reassembly (S.A.R.) circuit that contains a Direct Memory Access (D.M.A.) circuit for accessing an external storage. The SAR circuit is programmed so that when the VCI/VPI identifiers are representative of an Error Code Correcting procedure to be locally carried out in node, the SAR circuit performs a first DMA access which is decoded by an address decoder and used for controlling a Reed-Solomon coder and decoder. Conversely, when no ECC procedure is required in the node, the SAR decodes the corresponding VCI/VPI and performs a second DMA access which disables the Reed Solomon decoder.
Therefore, according to the requirements of the particular ATM session being established, there appears the capability to perform local ECC correcting procedures. Additionally, since the traditional SAR circuitsxe2x80x94ie components off the shelvesxe2x80x94may be used for embodying the invention, a simple and low cost hub having ECC capabilities can be designed. At last, the new hub remains fully compatible with the traditional hubs that form part of the ATM backbone network and which do not incorporate the ECC mechanism of the invention.